Whatever the accuracy of all those tables, they are probably confusing the OP more than answering the original question.
Most people will say out of the major agencies it doesn't matter a great deal which one you start with, as at the recreational level you can take any future classes with different agencies, and the instructor matters more. But the agencies do have differences in the ways they operate and what they cover in what certification, and CMAS is definitely a different beast than PADI, so it wouldn't hurt to understand all that. As far as international recognition, a certification from any major agency should be recognized anyplace. Anyplace you are likely to travel to dive, it's unlikely you will ever have trouble with a PADI card (unless maybe you want to dive in France?) I do think you may find the occasional shop in some place that is clueless about CMAS, but I don't know how likely this is to be an actual problem nowadays.
From the point of view of a business, the idea of offering a Groupon type deal is the hope of getting new customers and bringing in future business, since it's unlikely they're making much of anything between the deal and Groupon's cut. Lots of places don't really make money on their OW classes even at their regular price, they make it by selling gear. And it's somewhat common for scuba classes (even outside of any "deals") to quote a price that doesn't include everything, there could be extra charges for books, required gear purchases, gear rentals, OW dives, paperwork, all sorts of things. Perhaps if you post a pointer to the details of the specific deal/shop/class you are looking at people can comment on how it looks.
So if you want to learn to dive I'd look for a good place/instructor to get certified. If you can get a good deal that's great, but deals aren't always as good as they appear. And keep in mind that while there's lots of good ways to economize, scuba is not one of your cheaper activities.